this was from another thread when I asked the diff between m156 and m159

Originally Posted by MHP LLC

You can use SLS heads with a M156 intake manifold, they have 40mm int. valves and 34mm exhaust valves vs 40/33 for M156 heads, however ported M156 heads will flow better than stock SLS heads, so it's kind of a toss up as to which is more cost effective. Ported SLS heads would be the way to go but also the most expensive and we are talking about Maybe 10-15hp difference. The castings are just so good from the factory.

It has over 170 changes, dry sump, cams, rotating assembly, heads, intake manifold, TB placement, exhaust manifolds, etc. SLS's actually make 600HP stock. A good tune will net another 35HP+ or so. SLS is a 2013 viper chassis essentially so there's a lot more room under that hood plus the dry sump lowers the engine enough that the taller manifold fits. The rot assembly (crank, pistons, rods, rings) is .5 kilo lighter with P31/SLS bottom end vs M156 but static CR is the same 11.3:1 so all the power comes from software not the bottom end. Heads, cams will work but that's about it hardware wise.